This enzyme, isolated from the bacteria Rhodopseudomonas palustris and Zymomonas mobilis, participates, along with EC 2.5.1.103, presqualene diphosphate synthase, and EC 4.2.3.156, hydroxysqualene synthase, in the conversion of all-trans-farnesyl diphosphate to squalene. Eukaryotes achieve the same goal in a single step, catalysed by EC 2.5.1.21, squalene synthase.